The present invention relates to non-destructive characterization of sample systems, and more particularly to spectroscopic ellipsometer system(s) mediated methodology for quantifying thickness and impurity profile defining parameters in mathematical models of impurity profile containing thin membranes comprised of two substantially parallel surfaces which are separated by a thickness, wherein said spectroscopic ellipsometer system(s) operates in near-IR and IR wavelength ranges.
In view of developing open stencil lithography mask technology which utilizes open stencil lithography masks formed from thin silicon membranes, (which are typically formed by pn junction stop-etch techniques), a need exists for a non-destructive approach to characterizing thin membrane thickness and impurity profiles in impurity profile containing thin membranes comprised of two substantially parallel surfaces that are separated by a thickness of about 100 microns or less.
A Search of Patents has revealed U.S. Pat. No. 4,472,633 to Motooka which describes use of linearly polarized infrared light to investigate semiconductor wafers. Plots of Ellipsometric PSI vs. Ellipsometric DELTA, as a function of Angle of Incidence and/or Wavelength, for various carrier density profiles and depths are determined. Ellipsometric data obtained from a sample wafer is then utilized to plot Ellipsometric PSI vs. Ellipsometric DELTA, as a function of Angle of Incidence and/or Wavelength, and the results compared to the known plots. Close correlation between sample wafer and a known Ellipsometric PSI vs. Ellipsometric DELTA, as a function of Angle of Incidence and/or Wavelength, is indicative of the sample having a doping profile and depth similar to that of the wafer from which the known Ellipsometric PSI vs. Ellipsometric DELTA data was obtained. Data, is described as obtained utilizing monochromatic light, even though different wavelengths are used in succession where wavelength is the independent variable.
Another U.S. Pat. No. 4,807,994 to Felch et al., describes a non-ellipsometric method of mapping ion implant dose uniformity. Monochromatic Electromagnetic radiation with a bandwidth of not more than 1 nm, (chosen for sensitivity to sample parameters being measured), which has interacted with a sample in Reflectance or Transmission, is monitored by a Spectrophotometer and the results compared to previously obtained similar data regarding film thickness and ion implant doses, and similarities determined.
U.S. Pat. No. 5,900,633 to Solomon et al., describes a non-ellipsometric approach to analyzing patterned samples which involves irradiating a spot which includes first and second pattern regions, measuring eminating radiation, providing known reference spectrum/spectra and comparing measured spectral data thereto to evaluate parameters of layers in said two pattern regions.
U.S. Pat. No. 5,486,701 to Norton et al., describes a non-ellipsometric approach simultaneously utilizing wavelengths in both UV and Visible wavelength ranges to enable calculating a ratio thereof, which in turn is utilized to determine thin film thicknesses.
U.S. Pat. No. 6,049,220 to Borden et al., describes apparatus and method for evaluating semiconductor material. In a major implementation thereof, two beams are caused to illuminate a sample, one having energy above the bandgap and the other having energy near or below the bandgap. The second beam, after interaction with the sample, is monitored and change therein caused by said interaction is indicative of carrier concentration. It is noted that reflectance of an electromagnetic beam from a sample is a function of carrier concentration.
Known relevant art includes Articles, P-N Junction-Based Wafer Flow Process For Stencil Mask Fabricationxe2x80x9d, Rangelow et al., J. Vac. Sci. Technology B, November/December P. 3592 (1998); and xe2x80x9cApplication of IR Variable Angle Spectroscopic Ellipsometry To The Determination Of Free Carrier Concentration Depth Profilesxe2x80x9d, Tiwald et al., Thin Film Solids 313-314, P661, (1998).
In view of known prior art, there remains need for accuracy improving methodology for measuring impurity profiles in substrates, which methodology utilizes electromagnetic radiation with wavelengths in ranges for which the substrate is opaque and transparent, and which method involves utilizing data obtained both when electromagnetic radiation is caused to impinge on one surface, and then the other surface of said substrate.
In a basic sense, the present invention comprises a method of quantifying thickness and impurity profile defining parameters in impurity profile containing thin membranes, comprising providing an impurity profile containing thin membrane, and obtaining ellipsometric data from both first (front) and second (back) sides thereof, in combination with providing a mathematical model of said impurity profile defining parameters which comprises membrane thickness and impurity profile defining parameters, then regressing said mathematical model onto data obtained from both sides of said impurity profile containing thin membrane to evaluate said membrane thickness and impurity profile defining parameters. Note that this can include utilizing data in a procedure selected from the group consisting of:
utilizing the data sets obtained from front and back of the thin membrane simultaneously;
utilizing the data sets obtained from front and back of the thin membrane independently; and
utilizing the data sets obtained from front and back of the thin membrane both independently and simultaneously.
The present invention can more accurately be described as a method of quantifying thickness and impurity profile defining parameters in impurity profile containing thin membranes comprised of two substantially parallel surfaces that are separated by a thickness, wherein said method comprises, in any functional order, the steps of:
a. providing an impurity profile containing thin membrane comprised of two substantially parallel surfaces that are separated by a thickness, and providing a spectroscopic ellipsometer system capable of producing spectroscopic data sets at at least one angle of incidence of a beam of electromagnetic radiation to a surface of said impurity profile containing thin membrane when it is mounted in said spectroscopic ellipsometer system;
b. determining a range of wavelengths over which the impurity profile containing thin membrane is essentially transparent and the effect of the presence of said impurity profile has essentially negligible effect;
c. determining a range of wavelengths over which the impurity profile containing thin membrane is essentially transparent, but over which the effect of the presence of said impurity profile has a non-negligible effect;
d. utilizing substantially wavelengths in the range determined in step b., by an approach selected from the group consisting of:
reflection ellipsometry; and
transmission ellipsometry;
obtaining a spectroscopic data set;
e. utilizing substantially wavelengths in the range determined in step c., by reflection ellipsometry as applied to one surface of said impurity profile containing thin membrane, obtaining a spectroscopic data set;
f. utilizing substantially wavelengths in the range determined in step c., by reflection ellipsometry as applied to a surface of said impurity profile containing thin membrane offset from that utilized in step e. by said thickness, obtaining a spectroscopic data set;
g. providing a mathematical model for said impurity profile containing thin membrane including a parameter that quantifies thickness;
h. providing a mathematical model for said impurity profile containing thin membrane including parameters that quantify impurity profile defining parameters;
i. using the spectroscopic data set obtained in step d., regressing the mathematical model provided in step g. thereonto to evaluate the parameter that quantifies thickness;
j. using the thickness arrived at in step i. and the spectroscopic data sets obtained in at least one of the steps e. and f., simultaneously regressing the mathematical model provided in step h. thereonto to evaluate the parameters that quantify the impurity profile.
An alternative embodiment of the present invention method of quantifying thickness and impurity profile defining parameters in impurity profile containing thin membranes which are comprised of two substantially parallel surfaces that are separated by a thickness, can also be recited as comprising, in any functional order, the steps of:
a. providing an impurity profile containing thin membrane comprised of two substantially parallel surfaces that are separated by a thickness, and providing a spectroscopic ellipsometer system capable of producing spectroscopic data sets at at least one angle of incidence of a beam of electromagnetic radiation to a surface of said impurity profile containing thin membrane when it is mounted in said spectroscopic ellipsometer system;
b. determining a range of wavelengths over which the impurity profile containing thin membrane is essentially transparent and the effect of the presence of said impurity profile has essentially negligible effect;
c. determining a range of wavelengths over which the impurity profile containing thin membrane is essentially transparent, but over which the effect of the presence of said impurity profile has a non-negligible effect;
d. utilizing substantially wavelengths in the range determined in step b., by an approach selected from the group consisting of:
reflection ellipsometry; and
transmission ellipsometry;
obtaining a spectroscopic data set;
e. utilizing substantially wavelengths in the range determined in step c., by reflection ellipsometry as applied to one surface of said impurity profile containing thin membrane, obtaining a spectroscopic data set;
f. utilizing substantially wavelengths in the range determined in step c., by reflection ellipsometry as applied to a surface of said impurity profile containing thin membrane offset from that utilized in step e. by said thickness, obtaining a spectroscopic data set;
g. providing a mathematical model for said impurity profile containing thin membrane including parameters that quantify thickness and impurity profile defining parameters;
h. using all obtained spectroscopic data sets, simultaneously regressing the mathematical model thereonto to evaluate the parameters that quantify thickness and the impurity profile defining parameters.
The present invention will be better understood by reference to the Detailed description Section of this Specification, in conjunction with the Drawings.
It is therefore a purpose and/or objective of the present invention to teach a method of evaluating thickness and impurity profile describing parameters in an impurity profile containing thin film, wherein ellipsometric data is obtained from both sides of the impurity profile containing thin film, and a mathematical model which contains parameters which describe the thickness and impurity profile is then regressed onto data obtained from both said sides of the impurity profile containing thin film, separately and/or simultaneously.